The HbA1c test: what it shows about blood sugar over three months.

An HbA1c test measures how much glucose has attached to the haemoglobin in your red blood cells, which gives a picture of your average blood sugar over roughly the past two to three months. Unlike a single glucose reading, it does not swing with what you ate for breakfast, which is why doctors lean on it to understand longer-term blood sugar patterns.

For women with polycystic ovary syndrome, or with a family history of type 2 diabetes, it is one of the more useful numbers on a blood test form. Here is what it is, how to read it, and where it fits alongside your hormones.

How the HbA1c test works

Haemoglobin is the protein inside red blood cells that carries oxygen. Glucose in the bloodstream sticks to it slowly and steadily, a process called glycation. The more glucose circulating over time, the larger the share of haemoglobin that ends up with sugar attached. HbA1c is simply that share, reported either as a percentage or in mmol/mol.

Red blood cells live for around three to four months before the body replaces them, so the glycated haemoglobin in a sample reflects blood sugar across roughly that window. The most recent weeks count a little more than the earlier ones, because newer cells make up more of the sample.

• No fasting needed. Because it reflects months rather than hours, you can have it done at any time of day, fed or fasted.
• Stable from day to day. A stressful week or one big meal does not move it in any meaningful way.
• A simple blood draw. It is collected from a vein like most other tests, and often runs alongside cholesterol and other metabolic markers.

Why it matters in PCOS

Many women with PCOS have some degree of insulin resistance, meaning the body needs to produce more insulin than usual to move glucose out of the blood and into cells. Over years this can push blood sugar upward, and Australian and international guidelines recommend that women with PCOS have their glucose metabolism checked at diagnosis and then periodically, rather than waiting for symptoms.

Insulin resistance also feeds back into the hormonal picture. Higher insulin can nudge the ovaries to produce more androgens, which is one reason acne, excess hair growth and irregular cycles cluster together. Understanding where your blood sugar sits helps a doctor make sense of the whole pattern rather than one symptom at a time. Our PCOS and your hormones article walks through the hormonal side in more detail.

What the result can mean

Laboratories report HbA1c against bands rather than a single cut-off, and the exact reference ranges vary a little between laboratories. Broadly, a result is described as within the usual range, in a raised band that suggests higher-than-ideal average glucose, or in a band that is used, together with other information, when a doctor is assessing for diabetes.

• Within the usual range. Reassuring for now. If you have PCOS or other risk factors, a doctor will usually suggest rechecking every one to three years.
• Mildly raised. A prompt for a conversation about food, movement, sleep and family history, and for more regular monitoring. It is not a diagnosis on its own.
• Clearly raised. A doctor will normally confirm with a repeat test or a different glucose test before drawing any conclusion, then talk through what it means and what support is available.

A single number never tells the whole story. Your doctor reads HbA1c together with your fasting glucose if it was measured, your lipids, your weight history and your symptoms.

Things that can skew the reading

Because HbA1c depends on red blood cells living a normal lifespan, anything that changes how long those cells last can shift the result without blood sugar changing at all.

• Iron deficiency. Low iron can make red cells hang around longer, which may push HbA1c slightly higher than your true average glucose. This matters for women with heavy periods, so a doctor may check iron at the same time.
• Recent blood loss or anaemia. Faster cell turnover can make the result read lower.
• Pregnancy. Red cell turnover changes, so HbA1c is used differently during pregnancy and doctors rely more on glucose tolerance testing.
• Some haemoglobin variants. Inherited differences in haemoglobin, more common in some family backgrounds, can interfere with certain assays.

If any of these apply to you, tell the doctor reviewing your result. They may interpret it with more caution or suggest a fasting glucose instead.

HbA1c versus a fasting glucose test

The two tests answer different questions. A fasting glucose is a snapshot of one morning. HbA1c is the long exposure. Doctors often want both, because a person can have a normal fasting reading and a raised HbA1c, or the reverse, and the combination is more informative than either alone. An oral glucose tolerance test, where glucose is measured before and after a sugary drink, is a third option that some guidelines favour for women with PCOS because it can pick up changes earlier.

None of these is "better" in every situation. Which one a doctor orders depends on your history, your risk and what they are trying to understand.

Getting it done in Australia

When a GP orders HbA1c for a clinical reason, such as diabetes risk in PCOS, a Medicare rebate usually applies, although Medicare limits how often it can be claimed (generally once a year unless you already have diabetes). Tests you initiate yourself, without a clinical request, are self-pay and not rebated.

At KnowLuna you can bring your own doctor's request form and pay for the test only, or have a KnowLuna women's health doctor request the test and go through the result with you in a 20-minute video consult. Samples are collected at accredited collection centres, and a nurse home visit is available in some areas. You can see how a result is laid out on our sample report.

Common questions

Do I need to fast before an HbA1c test?

No. HbA1c reflects average glucose over months, so eating beforehand does not affect it. If other tests on the same form need fasting, such as fasting glucose or lipids, the collection centre will let you know.

How often should a woman with PCOS have her HbA1c checked?

Guidelines generally suggest checking glucose metabolism at diagnosis and then every one to three years, more often if the result was raised or if risk factors change. Your doctor will set a schedule that fits your situation.

Can HbA1c be normal even if I have insulin resistance?

Yes. Insulin resistance can be present for a long time while the body compensates and keeps glucose in range. That is why doctors look at the whole picture, including symptoms, weight distribution, lipids and sometimes a glucose tolerance test, rather than relying on HbA1c alone.

Does a raised HbA1c mean I have diabetes?

Not on its own. A doctor will usually repeat the test or use a second type of glucose test, and consider anything that might have affected the reading, before reaching any conclusion. A raised result is the start of a conversation.

General information only, not medical advice. If your symptoms are severe or sudden, see a doctor promptly.